REQUIRED PRACTICAL 2 : CULTURING MICROORGANISMS Flashcards
what is Bacterial culture is grown in?
a nutrient broth solution
what does the nutrient broth contain?
it contains all the nutrients that bacteria need to grow and divide
why is the broth cloudy?
it contains a very large number of bacteria
what is another way to cultural bacteria?
another way to culture bacteria is to use an agar gel plate
what do agar gel plates contain?
agar gel plates contain nutrient broth that’s been set into a jelly using a chemical called agar
what then happens to agar gel plates after being set into a jelly using a chemical called agar?
this is then poured into a petri dish and allowed to set
what do bacteria grow on an agar gel plate?
on an agar gel plate the bacteria grow divisible colonies
label where these are on a diagram
- agar gel
- petri dish
- bacterial colonies
petri dish is the dish holding the agar gel and bacterial colonies
agar gel is found with the petri dish like jelly
bacterial colonies are found on the agar gel
what can we do to to avoid contamination when making a nutrient broth solution? what does this do?
First, we sterilise all petri dishes, bacterial nutrient broth and agar.
This kills any unwanted microorganisms and prevents contamination
why can our cultures be easily contaminated?
because there are lots of microorganisms such as bacteria and fungi naturally in the environment, these can very easily contaminate our cultures
what is used to transfer bacteria into the culture.
an inoculating loop
what must we do before we use the inoculating loop? how do we do this?
we must sterilise the inoculating loop before transferring bacteria into the culture. we do this by passing the inoculating loop through a bunsen burner flame.
what do we do after transferring bacteria onto the dish?
next we attach the lid of the petri dish using adhesive tape. This stops the lid from falling off and unwanted microorganisms entering
what do we do after placing the lid of the petri dish? explain why.
after placing the lid of the petri dish on, we then place the agar plate upside down into an incubator. This stops moisture from dripping down onto the bacteria and disrupting the colonies
choosing the correct temperature:
in school labs, at what temperature do we normally incubate bacteria? Explain why we use this temperature.
25°C
Using this temperature, this reduces the chances that harmful bacteria will grow.
REQUIRED PRACTICAL: effect of antibiotics on bacterial growth
- Clean the bench with disinfectant solution. This kills microorganisms that could contaminate our culture.
- sterilise an inoculating loop by passing it through a bunsen burner flame.
- Open a sterile agar gel plate near a bunsen burner flame. The flame kills bacteria in the air
- Now we use the inoculating loop to spread the chosen bacteria evenly over the plate
- Place sterile filter paper discs containing antibiotic onto the plate
- incubate the plate at 25°C
After a few days, what results can we expect to see on our culture?
the bacteria forms a layer on the surface of the agar gel
around the antibiotic discs, we have a region where the bacteria have not grown. This is called the zone of inhibition
how can we measure the effect of the antibiotic?
by calculating the area of the zone of inhibition, to do that we use this equation =
area =3.142r^2
if radius is 12mm
calculate the area
area =3.142r^2
area =3.142 x12^2
area = 452.45mm^2
